/*
 * The MIT License
 *
 * Copyright 2012-2014 Zafar Khaja (zafarkhaja@gmail.com).
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 * */

package com.github.zafarkhaja.semver.expr;

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import com.github.zafarkhaja.semver.util.Stream;

/**
 * A lexer for the SemVer Expressions.
 *
 * @author Zafar Khaja (zafarkhaja@gmail.com)
 * @since 0.7.0
 */
class Lexer {

  /**
   * This class holds the information about lexemes in the input stream.
   */
  static class Token {

    /**
     * Valid token types.
     */
    enum Type implements Stream.ElementType<Token> {

      NUMERIC("0|[1-9][0-9]*"), DOT("\\."), HYPHEN("-"), EQUAL("="), NOT_EQUAL("!="), GREATER(
          ">(?!=)"), GREATER_EQUAL(">="), LESS("<(?!=)"), LESS_EQUAL("<="), TILDE("~"), STAR(
              "\\*"), AND("&"), OR("\\|"), NOT("!(?!=)"), LEFT_PAREN("\\("), RIGHT_PAREN(
                  "\\)"), WHITESPACE("\\s+"), EOL("?!");

      /**
       * A pattern matching this type.
       */
      final Pattern pattern;

      /**
       * Constructs a token type with a regular expression for the pattern.
       *
       * @param regexp
       *          the regular expression for the pattern
       * @see #pattern
       */
      private Type(String regexp) {
        pattern = Pattern.compile("^(" + regexp + ")");
      }

      /**
       * Returns the string representation of this type.
       *
       * @return the string representation of this type
       */
      @Override
      public String toString() {
        return name() + "(" + pattern + ")";
      }

      /**
       * {@inheritDoc}.
       */
      @Override
      public boolean isMatchedBy(Token token) {
        if (token == null) {
          return false;
        }
        return this == token.type;
      }
    }

    /**
     * The type of this token.
     */
    final Type type;

    /**
     * The lexeme of this token.
     */
    final String lexeme;

    /**
     * The position of this token.
     */
    final int position;

    /**
     * Constructs a {@code Token} instance with the type, lexeme and position.
     *
     * @param type
     *          the type of this token
     * @param lexeme
     *          the lexeme of this token
     * @param position
     *          the position of this token
     */
    Token(Type type, String lexeme, int position) {
      this.type = type;
      this.lexeme = (lexeme == null) ? "" : lexeme;
      this.position = position;
    }

    /**
     * {@inheritDoc}.
     */
    @Override
    public boolean equals(Object other) {
      if (this == other) {
        return true;
      }
      if (!(other instanceof Token)) {
        return false;
      }
      Token token = (Token) other;
      return type.equals(token.type) && lexeme.equals(token.lexeme) && position == token.position;
    }

    /**
     * {@inheritDoc}.
     */
    @Override
    public int hashCode() {
      int hash = 5;
      hash = 71 * hash + type.hashCode();
      hash = 71 * hash + lexeme.hashCode();
      hash = 71 * hash + position;
      return hash;
    }

    /**
     * Returns the string representation of this token.
     *
     * @return the string representation of this token
     */
    @Override
    public String toString() {
      return String.format("%s(%s) at position %d", type.name(), lexeme, position);
    }
  }

  /**
   * Constructs a {@code Lexer} instance.
   */
  Lexer() {

  }

  /**
   * Tokenizes the specified input string.
   *
   * @param input
   *          the input string to tokenize
   * @return a stream of tokens
   * @throws LexerException
   *           when encounters an illegal character
   */
  Stream<Token> tokenize(String input) {
    List<Token> tokens = new ArrayList<Token>();
    int tokenPos = 0;
    while (!input.isEmpty()) {
      boolean matched = false;
      for (Token.Type tokenType : Token.Type.values()) {
        Matcher matcher = tokenType.pattern.matcher(input);
        if (matcher.find()) {
          matched = true;
          input = matcher.replaceFirst("");
          if (tokenType != Token.Type.WHITESPACE) {
            tokens.add(new Token(tokenType, matcher.group(), tokenPos));
          }
          tokenPos += matcher.end();
          break;
        }
      }
      if (!matched) {
        throw new LexerException(input);
      }
    }
    tokens.add(new Token(Token.Type.EOL, null, tokenPos));
    return new Stream<Token>(tokens.toArray(new Token[tokens.size()]));
  }
}
